Leo Cullen says Leinster are itching to play tomorrow's Guinness PRO12 semi-final at the RDS against the Scarlets after reflecting on what might have been last weekend.

The Blues watched Clermont, who beat them in a close Champions Cup semi-final, lose to defending champs Saracens in the Edinburgh decider last Saturday.

Leinster don't want to miss out on another big final occasion, with the PRO12 final taking place at the Aviva Stadium at the end of the month.

"The ones you lose tend to stick in the memory more than the ones you win," head coach Cullen smiled at today's pre-match press conference.

"It's a different challenge this week, it's unusual preparation going into a semi-final having not played last weekend.

"Some of the guys who played against Ulster are still smarting (after the defeat at Kingspan Stadium) and feel they didn't quite do themselves justice and we didn't play at the level we can play.

"We were watching the Champions Cup final and we were wondering what could have been. This week is a relatively short week and I think at this stage guys are keen to get out there and play now.

"Everyone just wants to get back playing now. The players want to make it a special place to play at the RDS, and for most of the season it has been as the players have expressed themselves with the ball and hopefully tomorrow will be one of those special nights."

Leinster hammered the Scarlets 45-9 when the sides last met at the RDS in March but Cullen is cautious about what's ahead tomorrow, even if the loss of Scarlets' skipper Ken Owens with an ankle injury - "a key figure", according to the Leinster supremo - is a blow to the visitors.

"We lost against Scarlets over there as well," he pointed out. "We've had some good tussles with them in recent seasons and they're difficult to play against, they have a back row that plays on the edge all the time.

"If they get turnover ball they have the pace across the back line to cause team's problems. They will have been buoyed by their win away in Thomond as well, it's a different challenge but we've had a decent lead in and guys are just itching to play again."

Cullen explained his reasoning for leaving experienced Ireland lock Devin Toner on the bench, with Ross Molony and Hayden Triggs selected for the second row.

"He didn't train last week, he was carrying a knock from the Ulster game," said Cullen.

"But Hayden and Ross have gone well in combination with each other.

"I just think it's a competitive group, it's important that we finish strong in these games and Devin will give us good impact there."

Sean O'Brien is also named on the bench after recovering from a hamstring injury.

"He's making good progress," said Cullen.

"We're still managing Sean but he's coming back in. I think we've tried to go hard and pick a strong team, we have a strong set of reserves as well to represent Leinster well.

"After 22 regulation games and after using 51 players, competition is high and we had a lot of tough calls to make."

Hooker Sean Cronin is struggling to be fit for the decider, if Leinster make it.

"It's been quite difficult because his neck injury cropped up post the Clermont week, you're never really sure how the disc in the neck will settle down and we're trying to manage him carefully," Cullen explained.

"He was running this week but that leaves it tight for him for next week and he was left out of the (Ireland summer) tour."